A well-designed steel building, made with the right materials for its site and looked after, will serve you for decades. How many decades depends less on the brand on the quote and more on four things: the materials, the environment, the design details and the maintenance.
What the Building Code requires #
The Building Code’s durability clause, B2, sets minimum lives for building elements, assuming normal maintenance:
| Element | Minimum durability |
| Structure, and parts that are difficult to reach or replace | 50 years |
| Parts that are moderately difficult to reach or replace, such as roof and wall cladding | 15 years |
| Parts that are easy to reach and replace | 5 years |
Manufacturers state that pre-painted steel products, correctly installed and maintained, meet or exceed the 15-year B2 requirement for roofs and walls. Those are minimums, not life expectancies.
1. The materials #
Steelspan frames, purlins and girts are galvanised steel to Z275, meaning a zinc coating of 275 g per m², and our buildings are made with New Zealand steel. The zinc protects the steel underneath, and slowly weathers away instead of the steel. A thicker or more advanced coating lasts longer in harsh conditions, which is why cladding is chosen to suit the site.
2. Your environment #
Corrosion rates vary hugely around New Zealand. Industry guidance groups environments into corrosivity categories:
- Low (C2): mostly areas at least 50 km from the sea.
- Medium (C3): most coastal and urban areas, extending from roughly 1 km to 10–50 km inland from surf coasts.
- High (C4): mainly coastal, from several hundred metres to about 1 km inland.
- Very high and extreme (C5 and CX): beachfront and surf shorelines, and aggressive industrial sites.
Geothermal areas, and buildings with aggressive insides such as intensive animal housing, need special treatment.
3. Design details #
Good design keeps water moving and air flowing. Roof pitches that shed water, gutters with overflows, flashings that don’t trap dirt, and cladding kept clear of the ground all add years. So does avoiding contact between incompatible metals.
4. Maintenance #
Rain washes roofs, but walls and sheltered areas such as eaves, soffits and the underside of gutters don’t get rain-washed, so salt and dirt build up there. Manufacturers’ guidance recommends regular manual washing, more often near the coast. Our maintenance checklist post sets it out.
Our approach #
We believe you’re better served by an informed conversation about how your building will perform than by a long guarantee. We choose materials for your site’s environment, design out water traps, and explain exactly what maintenance keeps it performing. We’re happy to talk through how your building will meet the 50-year durability requirement for its structure.
In our 25+ years in the building industry, we’ve seen steel buildings still standing after 50 years. The materials have proven themselves, but every building also needs maintenance, and each site is different. We’ll explain what that means for yours.
Talk to Steelspan #
Tell us where you’re building and we’ll recommend the materials that suit that site. Use our Easy Shed Quote or call 0800 787 726.
